Lasers are used in various testing and research operations. For example, lasers may be used as light sources in the photographic recording of flow fields, such as in internal combustion engines, wind chambers, heating and cooling system ducts, or other applications where fluid flow is of interest. In these applications, a laser system may provide a double pulse of laser light for illumination to allow photographic recording of rapid fluid flow in the particular device. These applications often require two pulses of light within 5 to 60 microseconds of each other. Heretofore, two lasers were typically used in a laser system to provide pulses in such rapid succession. However, these systems are relatively expensive because two lasers are needed.
To provide background, the principles of operation of an exemplary laser, e.g., a Nd:YAG laser, may be described as follows. The laser is generally comprised of flash lamps, laser rods, mirrors for reflecting laser light from the rods, and a Q-switch which enables the storage of energy in and dumping of energy out of the laser rods. The Q-switch is typically comprised of a Pockels cell, a Glan-Taylor polarizer prism and a Q-switch driver circuit. A capacitor bank is charged by a high voltage power supply to store energy for the flash lamp.
When a fire signal or triggering signal is provided to the laser, a capacitor bank discharges power through the flash lamps and ionizes the flash lamps. The light energy from the flash lamps pump Neodymium (Nd) atoms in the oscillator and amplifier rods to higher energy levels. The Q-switch driver circuit then triggers the Pockels cell by providing a high voltage signal. The Pockels cell changes its polarization angle in response to the high voltage signal to allow passage of photons to allow lasing to occur. The Neodymium atoms emit photons coherently as they fall back to a lower energy level.
Generally, the Q-switch driver circuit is unable to provide high voltage pulses to the Pockels cell in extremely rapid succession, at the rate required for very fast photography, due to constraints such as the time required to charge capacitors in the Q-switch driver circuit.
U.S. Pat. No. 3,783,403, issued to Hook et al. on Jan. 1, 1974, describes a laser system for producing double pulses from a single laser. The system utilizes two flash lamp trigger circuits and a Q-switch driver circuit including two pulse inputs to a high voltage pulse transformer. The circuit provides two laser pulses with variable pulse intervals ranging from 80 microseconds to 2,000 microseconds.